The present invention relates to a catheter for use in the vascular system and, more particularly, to such a catheter which is formed with pressure responsive valves therein.
Catheters for delivery of fluids into the vascular system are known in the art. These catheters include a catheter lumen having a proximal end through which material is introduced into the catheter lumen and a distal end from which fluid exits from the catheter lumen. Some catheters are formed with a single distal end hole which serves both as a means of egress for the fluid and a passageway through which a guide wire can fit. In addition to an end hole some catheters are formed with multiple side holes. The provision of multiple side holes permits better mixing of fluid with blood, avoids a strong end hole jet, and permits a slightly higher flow rate. Some catheters with side holes have no end hole. Without an end hole the catheter cannot be used with a guide wire.
Catheters with multiple side holes may have problems with uniform fluid distribution. Additionally, multiple side holes create a problem where the guide wire may inadvertently exit from a side hole instead of from the end hole. Further, and especially where non-ionic contrast media is used, blood tends to clot at the side holes, which may cause delivery problems. Further, side holes are completely open and vulnerable to the ambient conditions surrounding them. Thus, when the catheter is in the vascular system it is possible, even at low pressure gradient, to get blood flow through the side holes into the catheter creating the possibility of clot formation in the side hole. Further, the use of multiple side holes can cause the outer wall of the catheter to be less smooth than desired resulting in an inadvertent gouging of the tissue. This is a bigger problem where the catheter is introduced at a site remote from the site where the fluid is to be delivered.
Catheters formed with slits, instead of holes, in the distal segment of the catheter are known in the art. The provision of slits in lieu of holes is intended to overcome some of the problems created by catheters with multiple side holes. A catheter formed with distal slits is disclosed in U.S. Pat. No. 3,888,249 issued to David L. Spencer on Jun. 10, 1975. The Spencer Patent disclosed a catheter for infusion of medication into an artery. The medication flows through the catheter lumen and exits into the artery through the distal slits which act as valves. The '249 catheter has a double wall in the area of the slits. It includes an inner wall with windows formed therein and an outer wall formed with slits therein. The slits overlie the windows. The modulus of elasticity of the outer wall is less than the modulus of elasticity of the inner wall and this difference in the elasticity of the two walls permit the slit/window combination to act as a valve. Another example of a catheter formed with slits rather than holes is disclosed in U.S. Pat. No. 4,973,319 issued to Gerald S. Melski on Nov. 27, 1990. The Melski Patent discloses a catheter for infusing fluids into a vein or artery. The fluids to be infused are therapeutic agents or nutrients. The Melski catheter, like the Spencer catheter, has a double wall in the area of the slits. The Melski catheter has an inner wall with apertures formed therein covered by an outer wall with slits formed therein. Melski discloses the use of a medical grade silicone rubber for both his inner and outer wall. However, Melski makes it clear that the inner wall should be made of a stiffer material than the outer wall in order for the two walls to work together to provide a one-way valve.
The catheters disclosed in the '249 and '319 patents may prove useful for delivering fluids at low pressure into the vasculature. Where a high pressure delivery is needed, however, the use of two walls to create the valve makes the valve incapable of withstanding repeated high pressure and/or high velocity injections. The walls may delaminate under these circumstances and the catheter would fail. An additional problem with the two walled construction described in these patents is that they have a step on the exterior surface of the catheter, where the inner tube fits into the outer tube, and this step provides a location for clot formation. An additional problem with the catheters disclosed in these patents is that they are relatively expensive to manufacture and fluid distribution problems may arise if the windows and slits are not properly aligned.
When catheters are used for certain procedures it is desirable to insert the catheter at a site remote from the site where the fluid is to be injected. In such cases the catheter must be steered through the somewhat tortuous vasculature. In order to so do, the catheter itself must possess sufficient stiffness, torqueability, and pushability. In the alternative the catheter may be constructed for use with a guide wire, the guide wire providing the needed stiffness, torqueability, and pushability characteristics. Where a guide wire is to be used with a catheter, the catheter must be provided with an end hole. However, end holes can create problems when it is desired to deliver fluid with a uniform distribution along the length of the distal portion of the catheter.
Thrombolysis involves the dissolving of blood clots in the vascular system. There are a large number of people who need to have such blood clots dissolved. It has been proposed that the blood clots could be more efficiently lysed if the lytic agent were delivered to the clot at high velocity using a forceful injection. This would reduce the time needed to complete the procedure.
For optimal lysing, the lytic agent should be delivered at an even flow rate at the desired high pressure required for high velocity impact from exits provided along a predetermined length of catheter. Yet this high pressure/even flow rate function must be provided by a catheter which prevents back flow of blood into the catheter at ambient pressure.
It is an object of this invention to provide a catheter which provides the high pressure/even flow input function while meeting the other necessary objectives of such a catheter including preventing back flow of blood into the catheter at ambient pressure and providing a design which is capable of being steered through the vascular system.
It is a related purpose of this invention to provide this objective in a catheter which is relatively inexpensive to manufacture.